1. Field of the Invention
The present invention relates to an electromagnetic projectile launcher, and in particular, to an electromagnetic projectile launcher wherein the projectile is continuously accelerated to a high velocity in a very efficient manner involving minimal physical contact and essentially no electrical conductivity between the launcher and the projectile.
2. Description of the Background Art
Known electromagnetic accelerators have been designed to accelerate and launch projectiles at high velocities. An example of such an electromagnetic accelerator is a rail gun, which consists of parallel conductive sliding or rolling rails and a conductive projectile riding along such conductive rails, which together form a closed electrical circuit. When the parallel conductive rails are connected to a power supply, the conductive sliding or rolling rails allow a large electric current to pass through the projectile. Electric current runs from one terminal of the power supply, up one conductive rail, across the projectile and down the other conductive rail to the other terminal of the power supply. This flow of the current creates a powerful magnetic field between the conductive rails and up to the projectile. This magnetic field in connection with the current across the projectile creates a Lorentz force which substantially continuously accelerates the projectile along the rails away from the power supply.
An example of such a rail gun is found in U.S. Pat. No. 6,662,713 to Thomas, which discloses a rail gun which uses magnetic forces to accelerate a round held within the firing chamber of a gun. A pair of rails extend along a length of the firing chamber and each has at least one wire passing therethrough. At least one toroid magnet encompasses the rails as does a solenoid magnet. The wires within the rails, the toroid magnet and the solenoid magnet are each electrically coupled to an electrical source with electrical communication established by a trigger. A magnetically sensitive round held within the firing chamber is initially accelerated by the rails, then further accelerated by the toroid magnet and then further accelerated by the solenoid magnet prior to being discharged from the firing chamber.
While rail guns are in principle very simple, they have several known disadvantages, making them practically difficult. One known disadvantage is that, since the projectile must be in constant physical contact and electrical conductivity with the rails to let electric current flow as the projectile is being launched, large amounts of heat are generated between the moving projectile and the rails which burns the rails thereby causing significant and rapid wear of the rails. Thus, many rail guns can only be used for a single application or a small number of applications due to the damaged to the rails.
In order to avoid the direct physical contact between the rails and the projectile, another type of rail gun uses plasma arcing. As with the conventional rail guns described above, a rail gun which uses plasma arcing is composed of two parallel arranged current-conducting rails which are connected with a high-intensity current source. To accelerate the projectile, the trailing end of the projectile has an armature that acts as a current bridge between the two rails. Plasma is used to constitute the armature (plasma armature). As with the conventional rail gun, current flows from the large power supply through one rail and through the electric arc, down the other rail and back to the power supply. Again, a magnetic field is generated in this current loop which causes an electromagnetic force (Lorentz force) thereby accelerating the arc and thus also the projectile in front of the arc. However, while plasma arcing allows for the projectile to not come directly into contact with the rails, a rail gun using a plasma armature generates an even higher amount of heat than a conventional rail gun, again, damaging the rails.
Another disadvantage of using a rail gun is that rail guns require an extremely high current DC power source. Rail guns require the current flowing through the rails and the projectile to be in the magnitude of tens of thousands to millions of amperes in order to generate the high velocity of the projectile which is sought. Further, the extremely high current is required to be generated over a very short period of time. Without such a high current generated over such a short period of time, the projectile would fail to be launched at an appropriate velocity. Thus, a power supply which can generate such a high amount of current over such a short period of time is both large in size and expensive.
A second example of an electromagnetic accelerator is a coilgun. A coilgun consists of one or more coils arranged along a barrel with a projectile placed at one end. A high-intensity power supply is attached to one end of the coil or coils and a large electric current is pulsed through the coil or coils. The electrical current running through the coil creates a large magnetic field which pulls the projectile to the center of the coil. An electrical current running through a coil which thereby creates a magnetic field is called an electromagnet. Once the projectile is near the center of the electromagnet, the current being supplied to the coil is shut off, and the next electromagnet is turned on such that the projectile is then pulled toward the center of the next electromagnet. This process of switching on and off the electromagnets is repeated with each coil along the barrel of the coilgun until the projectile moves at an appropriate speed and is launched from the coilgun. The switching on and off of the electromagnets within the coil guns occurs at a rapid pace so as to ensure that the projectile is accelerated quickly along the barrel.
Coilguns are beneficial in that coilguns have no sliding contact with the projectile, such that no wear or erosion occurs to the barrel except some physical restraint to keep the projectile along the center, and the working life of a coilgun is potentially infinite, unlike the working life of a rail gun.
However, there are other disadvantages associated therewith. For example, a known disadvantage of coilguns is the switching of the power through the coils. Each coil inherently has a certain substantial amount of inductance which will prevent precision switching between on and off of the power to the coils. As such, a precision control circuit to turn on and off each coil depending on the position of the projectile must be added to the coilgun.
Another disadvantage of a coilgun is that since the magnetic coil attracts the magnetic material (projectile) toward the center of the coil, each coil only attracts the projectile for substantially half the length of the coil and the projectile travels by itself the remaining half/portion of the coil. As such, a coilgun has segmented acceleration, causing the projectile to begin slowing down before being accelerated again by the next coil. This is inherently inefficient.
A further disadvantage of a coilgun is the rate at which the projectile becomes saturated by the magnetic field and the rate at which it loses its magnetic saturation. Once an object becomes saturated, the amount of force by which it can be attracted stops increasing. The rate at which the projectile loses its saturation is a critical factor. As this rate is constant, greater distances between drive electromagnets are needed to compensate for this rate, and as the projectile increases in speed it reaches drive electromagnets at progressively faster rates. Without compensation for desaturation time, there will be less and less affect on the velocity of the projectile per coil, resulting in significantly lower efficiency per drive electromagnet stage as the projectile travels down the line. Once the amount of force exerted to the projectile is less than or equal to the amount of resistance exerted on the projectile due to air friction, friction in the barrel, etc., the projectile will no longer accelerate.
Still further, other known electromagnetic launchers include induction coil launchers, such as ring launchers or eddy-current launchers. Induction coil launchers create an induced current on the projectile which repels the source current within the body of the induction coil launcher. The induced current on the projectile causes the projectile to move towards the lesser reaction thereby pushing the projectile forward. While the induction coil launcher initially quickly accelerates the projectile, induction coil launchers have the disadvantage that the projectile decelerates before being lunched.
Although some of the disadvantages of conventional electromagnetic launching systems have been addressed, as discussed above, a need still exists in the art for an improved, more efficient electromagnetic launching system which more completely addresses all of the disadvantages attendant the conventional systems. In particular, there is a need for such an improved system that may continuously and efficiently accelerate a projectile but which does not involve electrical contact between the projectile and the rails of the launcher so as to ensure a long working life and permit the use of a comparatively smaller power supply.